Method of feeding continuous-casting machines using controlled gas pressure head

ABSTRACT

A tundish formed as a fully enclosed refractory-lined vessel for feeding molten metal to a continuous-casting machine. The vessel is mounted to tilt and has a nozzle in the bottom and the top is connected to a ladle by a pressure-tight bellows. The vessel is pressurized through a dynamic pressure regulator which controls the effective head at the nozzle.

United States Patent 91 Lyman [4 1 July 3,1973

[ METHOD OF FEEDING CONTINUOUS-CASTING MACHINES USING CONTROLLED GAS PRESSURE HEAD [75] Inventor: Richard E. Lyman, Rich Township,

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

[22] Filed: Sept. 10, i971 [21] Appl. No.: 179,402

[52] U.S. Cl 222/1, 164/281, 222/152,

222/166 [51] Int. Cl 822d 37/00 [58] Field of Search 222/152, 1, 166,

222/DIG. 8, DIG. 13, DIG. l5, DIG. 1; 164/281, 334, 335, 336

[56] References Cited UNITED STATES PATENTS 2,568,525 9/1951 Waddington et a1. 222/D1G. 1

3/1971 Shapland 222/D1G. 13 2,889,597 6/1959 Griffiths 164/335 3,524,494 8/ 1970 Smith ZZZ/DIG. 8 3,599,831 8/1971 Harvill et a1. 222/DIG. 13

Primary Examiner-Robert 'B. Reeves Assistant Examiner-David A. Scherbel Attorney-Ralph H. Dougherty et a1.

[5 7] ABSTRACT A tundish formed as a fully enclosed refractory-lined vessel for feeding molten metal to a continuous-casting machine. The vessel is mounted to tilt and has a nozzle in the bottom and the top is connected to a ladle by a pressure-tight bellows. The vessel is pressurized through a dynamic pressure regulator which controls the effective head at the nozzle.

2 Claims, 3 Drawing Figures PATENTEDJUL 3 I973 SNEEI 2 0F 2 T0 VA CUUM PUMP F/G. 3. ii

INERT GAS IN 47 ACTUATOR INVENTOR. RICHARD E LYMAN T0 TU/VD/Sl'l A t rarney METHOD OF FEEDING CONTINUOUS-CASTING MACHINES USING CONTROLLED GAS PRESSURE HEAD This invention relates to an improved tundish construction and method of feeding molten metal to a continuous-casting machine.

Although my invention is not thus limited, my tundish and method are particularly useful for feeding molten metal to a vertical continuous-casting machine. In continuous casting, it is important to control the rate of feeding. Provision also should be made for shutting off the flow of metal to the mold very quickly. My invention effectively achieves these objectives.

An object of my invention is to provide an improved tundish construction and feeding method which assure that the molten metal feed rate can be controlled.

A further object is to provide a tundish and method which enable the flow of molten metal from the tundish to be shut off quickly without causing the metal to freeze at the pouring nozzle nor to drip or spray into the casting cavity and form solid hangers.

A further object is to provide an improved tilting tundish which is equipped with a dynamic pressure regulator for controlling the pouring rate.

FIG. 1 is an elevation view of my improved tundish installed on a continuous-casting machine.

FIG. 2 is a sectional view taken along line II-II in FIG. 1.

FIG. 3 is a vertical sectional view on a larger scale of my dynamic pressure regulator.

FIG. 1 shows diagrammatically a portion of a continuous casting machine which includes an open ended, water-cooled oscillating mold 10. Machines of this type apart from my novel tundish are known; hence no more detailed description is deemed necessary.

In accordance with my invention, a fixed support structure 12 has rails 14 mounted thereon. A tundish 15 has carriage wheels 16 and 17 mounted for movement along rails 14, and a tilting frame 18 mounted on one end of the tundish, preferably of structural steel members. Means for effecting horizontal movement of the tundish such as a double-acting hydraulic cylinder 19 is connected to the fixed support 12 and to tundish 1S. Cylinder 19 can be omitted and wheels 16 driven to provide horizontal movement of the tundish. A hydraulic cylinder-21 is attached to the base of support structure 12 and contains a reciprocable piston and piston rod 22 which engages the tilting frame 18 for tilting the tundish about the axis of the rear support wheel 16. Hydraulic cylinder 21 may be replaced by any jacktype device, and may be installed to bear against the ground while fixed to the tundish or vice versa. Further, it could be replaced by an overhead hoist mechanism.

Tundish 15 has the form of a fully enclosed vessel and includes a steel shell 25 and a refractory lining. I prefer to make up the lining of a layer 26 of ordinary fire clay brick, an intermediate layer 27 of low-density insulating refractory, such as bubbled alumina, and an innermost working layer 28 of high magnesia or high alumina content. The shell and lining have an outlet opening 30 which leads to a nozzle 32 at the lower edge of the tundish adjacent the casting machine and an inlet opening 33 on the top wall of the tundish remote from the nozzle. I mount a bellows 34 around the inlet opening, which bellows is adapted to be fastened to a pouring ladle 36. This provides a gas-tight seal between the ladle and the tundish.

The top wall of the tundish also has a port 43 in which I removably mount a dynamic pressure regulator 44.

As FIG. 3 shows, this pressure regulator includes three tees 45, 46, 47, a nipple 48 connecting two arms of tees 45 and 46, a nipple 49 connecting two arms of tees 46 and 47, and plugs and 51 closing the outer arms of tees 45 and 47. The leg of tee 46 communicates with port 43 of the tundish. I connect the leg of tee 45 to a source of inert gas (usually argon) under pressure, and the leg of tee 47 preferably to a vacuum pump, although it may simply discharge to the atmosphere. Nipples 48 and 49 contain variable opening valve sleeves 52 and 53, respectively. An operating stem 54 extends through the assemblage of tees and nipples and out the plugs 50 and 51 at each end of the assemblage. The stem carries valve discs 55 and 56 within sleeves 52 and 53, respectively. The midportion of the stem includes an adjusting sleeve 57 for varying the relative position of the two discs. I connect one end of the stem to a suitable actuator (not shown). The central tee 46 carries a pressure gage 58 located between the two discs. This pressure gage could also be connected to some other port entering the vessel.

According to my feeding method, I start with the piston rod 22 extended from its cylinder 21 and frame 20 and tundish 15 tilted as shown in phantom lines in FIG. 1. I preheat the inside of the tundish, preferably to a temperature of about 2,700 to 3,000F. Conveniently I use the burner and follow the procedure described and claimed in my US Pat. No. 3,480,376 in preheating. I may either remove the pressure regulator 44 and insert the preheating burner through port 43, or I may permanently install the burner in the port and connect the regulator through the sight opening of the burner. I pour molten metal into the tundish through the bellows 34 to a level just below the nozzle outlet. Next I retract piston rod 22 and thus tilt frame 18 and tundish 15 until they are level. Wheel 17 is in contact with rail 14 when the tundish is level. Molten metal feeds through the nozzle 32 into oscillating mold 10 of the casting machine. I may remove the nozzle after each cast for the necessary maintenance.

As the tundish feeds metal to the casting machine, I pour additional metal through the bellows 34 to replace that which discharges, taking care to retain the pressure seal. The dynamic pressure regulator 44 acts to maintain the desired effective head acting on the metal in the tundish irrespective of the level of molten metal therein. Its action is analogous to that of a centertapped voltage divider in an electric circuit.

This regulator is a piping arrangement with connections to a pressure tank, a vacuum receiver, and an intermediate connection to the tundish. An adjustable gas-flow impedance is provided in the piping between the tundish connection and the pressure tank connection. A similar impedance is provided between the tundish and the vacuum receiver. These impedances are controlled by a common linkage in such a manner that when one impedance is increased, the other is decreased and vice versa. A continual flow of inert gas such as argon is maintained between the pressure tank and the vacuum receiver. The pressure within the tundish is maintained at some value between the pressures of the pressure tank and the vacuum receiver depending on the values of the adjustable impedances and the corresponding pressure drops across these components. If, for example, the impedance adjacent to the pressure tank is adjusted to a very low value and the impedance adjacent to the vacuum receiver is adjusted to a high value, the tundish pressure will approach that of the pressure tank. When the tundish pressure is not undergoing adjustment, the gas flow between the pressure tank and the vacuum receiver will remain nearly constant. During tundish pressure adjustment, flow of gas into or out of the tundish, as the case may be, proceeds rapidly because the pressure tank and vacuum receiver are sized adequately relative to the volume of the tundish. The control response of the dynamic regulator is therefore much faster than the response of a conventional static pressure regulator.

A preferred embodiment of the dynamic pressure regulator is shown in FIG. 3. A varying portion of gas which enters tee 45 acts to pressurize the tundish, while the remainder discharges through tee 47. The relative position of stem 54 determines the pressure applied to the tundish. When the stem moves toward the left, the area of the opening through valve sleeve 52 increases, while the area of the opening through valve sleeve 53 diminishes. Thus more gas is admitted to the regulator and there is more resistance to its escape, whereby the pressure applied to the tundish rises. The reverse action takes place when the stem moves toward the right. When a steady state condition is reached in the tundish, gas flow is direct from the pressure source to the vacuum receiver. I may simply observe the pressure as indicated on gage 58 and manually adjust the stem position, or I may include suitable automatic mechanism. Whenever a drastic change in the feed rate is needed for the casting machine to operate properly, I can effect such change very quickly by adjusting the regulator appropriately. Whenever I wish to stop feeding metal to the casting machine, I can operate cylinder 21 to tilt the tundish up and away from the machine, stopping the flow of metal through nozzle 32.

From the foregoing description, it is seen that my invention affords a simple tundish construction which assures complete control of feeding metal to a continuous-casting machine.

I claim:

1. A method of feeding molten metal to a continuouscasting machine from a tundish, said tundish comprismg:

an enclosed refractory lined vessel,

means supporting said vessel,

a nozzle mounted in the bottom wall of said vessel,

means carried by the top wall of said vessel remote from said nozzle for introducing molten metal to the vessel and including means for effecting a gastight seal through said introducing means,

pivoting means engaging said vessel for pivoting said vessel about a horizontal axis,

source of inert gas under pressure, and

a dynamic pressure regulator connected to said source and to said vessel for pressurizing said vessel and controlling the pressure therein; said method comprising:

tilting said tundish to raise the elevation of said nozzle,

introducing molten metal to the tundish until it reaches the level of the nozzle,

returning the tundish to a horizontal position to pour the metal through said noule into the casting machine, and

pressurizing the tundish with inert gas introduced through said regulator and introducing additional metal to said tundish to replace that poured through said nozzle to maintain a head of steel above said nozzle at all times during the pouring.

2. A method of maintaining the height of a liquid in a gas-tight bottom pour vessel during pouring, said method comprising:

introducing the liquid to the vessel through a gastight inlet construction;

causing a liquid pool to form in the vessel;

effecting a gas-tight seal through the pouring nozzle by causing the liquid pool to rise to a sufficient height to block off gas flow through the nozzle;

pressurizing the vessel with gas when the liquid level rises above the desired level by introducing gas to the vessel through a pressure regulator comprising: an elongated chamber; an operating stem extending longitudinally therethrough; a pair of valves comprising variable-opening valve sleeves and a pair of valve discs fixed on said stern and each movable in one of said valve sleeves; a connecting means communicating with a pressure source; a connecting means communicating with a vacuum receiver; and a central connecting means connected between the two valves and communicating with the interior of said vessel;

reducing the pressure by opening said pressure regulator to said vacuum receiver when the liquid level falls below the desired level; and

introducing additional liquid to the vessel to replace that poured through the nozzle. 

2. A method of maintaining the height of a liquid in a gas-tight bottom pour vessel during pouring, said method comprising: introducing the liquid to the vessel through a gas-tight inlet construction; causing a liquid pool to form in the vessel; effecting a gas-tight seal through the pouring nozzle by causing the liquid pool to rise to a sufficient height to block off gas flow through the nozzle; pressurizing the vessel with gas when the liquid level rises above the desired level by introducing gas to the vessel through a pressure regulator comprisinG: an elongated chamber; an operating stem extending longitudinally therethrough; a pair of valves comprising variable-opening valve sleeves and a pair of valve discs fixed on said stem and each movable in one of said valve sleeves; a connecting means communicating with a pressure source; a connecting means communicating with a vacuum receiver; and a central connecting means connected between the two valves and communicating with the interior of said vessel; reducing the pressure by opening said pressure regulator to said vacuum receiver when the liquid level falls below the desired level; and introducing additional liquid to the vessel to replace that poured through the nozzle. 